a. Field of the Invention
This invention relates to an ultrasonic thickness measuring method and apparatus in which a probe placed in contact with a material to be measured transmits an ultrasonic pulse and detects reflection pulses from the material to measure the time of travel of the ultrasonic pulse through the material for obtaining a thickness of the material and it further relates to a check apparatus used with the ultrasonic thickness measuring apparatus for checking an operation condition of the apparatus. More particularly, this invention relates to an ultrasonic thickness measuring method and apparatus suitable for measuring a thickness of the material by using multiple reflection pulses and a check apparatus suitable for the method and apparatus.
b. Related Arts
FIG. 6 is a block diagram showing one form of a conventional ultrasonic thickness measuring apparatus.
In the figure, 101 is a synchronizing circuit generating a synchronizing pulse for determining an ultrasonic pulse transmission timing, 102 is a transmitting circuit generating electric pulse for energizing a probe, 103 is the probe for transmitting and receiving ultrasonic pulses, 104 is a receiving circuit receiving and amplifying multiple echo or reflection pulses, 112 is a second clock circuit generating a clock pulse indicative of a unit time, 113 is a third AND gate selecting the clock pulse, 114 is a counter circuit counting pulses output from the third AND gate 113, 115 is a digital indicator, 116 is a material to be measured which is coated with a couplant and placed in contact with the probe 103 to be subjected to thickness measurement, 117 is a control circuit for controlling delay of reflection pulse receiving and controlling a gain, and 118 is a CRT display indicating multiple reflection pulses.
With this arrangement, the conventional ultrasonic thickness measuring apparatus will operate as follows:
An ultrasonic pulse transmitted from the probe 103 in response to a synchronizing pulse which is output from the synchronizing circuit 101 is subjected to multiple reflection between a bottom and a surface of the material to be measured. The reflection pulses are received by the receiving circuit 104 and a measuring gate is provided by a second flip-flop circuit 111 in such a way that a period between one reflection pulse and a next reflection pulse is kept high. The reflection pulses are indicated on the CRT display 118.
At this time, receiving gain control or gate delaying control is carried out by the control circuit 117 so as to minimize interference of undesired signals into the multiple reflection pulses.
Further, sweep traces of the CRT display 118 are adjusted to check the indication position of the reflection pulses and the measuring range.
FIG. 7 shows operating waveforms for the conventional ultrasonic thickness measuring apparatus. In the figure, .circle.10 to .circle.12 indicate waveforms appearing at positions denoted by corresponding numerals in the circuit of FIG. 6. .circle.10 shows a transmission pulse T and a first reflection B1 and a second reflection pulse B2 from the bottom of the material 116 to be measured. .circle.11 shows a measuring gate of a rectangular signal proportional to a time interval between the first reflection pulse B1 and the second reflection pulse B2 output from the second flip-flop circuit 11. .circle.12 shows "and" output pulse of the measuring gate and the clock pulses indicative of the unit time. The output pulses are counted and the thickness measurement results for the material 116 to be measured are presented on the digital indicator 115.
The conventional ultrasonic thickness measuring apparatus as described above further has the CRT display 118 for selecting multiple reflection pulses from the material 116 to be measured. More particularly, the gate may be adjusted by monitoring the CRT display 118 to minimize interfering signals such as noises or other undesired signals. Checking of the indication position of the reflection pulses and the measuring range is also carried out.
The thickness measurement is effected by using a measuring gate corresponding to a time interval between the first reflection pulse B1 and the second reflection pulse B2. In this case, the second reflection pulse B2 is detected by visually discriminating it among the received signals indicated at equal intervals on the CRT display.
This conventional ultrasonic thickness measuring method or apparatus has another disadvantage that normal measurement is prevented by damped oscillation of the first reflection pulse B1 or delayed signals generated between the first reflection pulse B1 and the second reflection pulse B2 and appearing through other propagation paths.
The present invention is made to overcome the disadvantages involved in the conventional technique and it is an object of the present invention to provide an ultrasonic thickness measuring method and apparatus of a reduced size and weight which is capable of automatically eliminating undesired signals and capable of effecting accurate thickness measurement, without providing the CRT display, by using multiple reflection pulses of less interference or noises.
There has been another form of ultrasonic thickness measuring apparatus which employs a probe with a delay member.
FIG. 10 illustrates one example of the conventional ultrasonic thickness measuring apparatus of the type. In the figure, 201 is a synchronizing circuit generating a timing signal for ultrasonic pulse transmission, 202 is a transmitting circuit energizing a probe, 203 is the probe with a delay member such as a delay line, 204 is a material to be measured which is coated with a couplant such as oil and placed in contact with the probe 203 having the delay member to measure the thickness, 205 is a receiving circuit receiving and amplifying multiple reflection pulses from the material 204 to be measured, 220 is a flip-flop circuit outputting a measuring gate having a width corresponding to a time interval of the reflection pulses output from the receiving circuit, 219 is a control circuit controlling a receiving gain of the receiving circuit 205 or an operation of the flip-flop circuit 220, 221 is a CRT display presenting an A scope waveform output from the receiving circuit 205, 222 is a second clock circuit generating clock pulse signals, 223 is an AND gate outputting "and" of the output from the flip-flop circuit 220 and the clock signals, 224 is a counter for counting the number of pulses output from the AND gate 223, and 225 is an indicating circuit for indicating the counting results.
In the conventional ultrasonic thickness measuring apparatus arranged as described above, an ultrasonic pulse transmitted to the material 204 to be measured from the probe 203 with the delay member by a timing signal output from the synchronizing circuit 201 travels through the delay member made for example of an acrylic material and is incident upon the material 204 to cause multiple reflection between a surface and a bottom of the material 204. The reflection pulses from the material 204 are amplified by the receiving circuit 205 and presented on the CRT display 221. At this time, the control circuit 219 controls the reception gain or operation of the flip-flop circuit 220 to minimize interference of undesired signals such as parastic signals for the transmission pulse or reflection pulses from the surface of the material with the multiple reflection pulses within the material 204 to be measured.
Further, sweep trace of the CRT display 221 is adjusted to check the indication position of the reflection pulse or measuring range.
FIG. 11 shows an example of operation waveform in the conventional ultrasonic thickness measuring apparatus. .circle.15 includes a transmission pulse T together with a first surface reflection pulse S1 from the surface of the material 204 to be measured, a first bottom reflection pulse B1 and a second bottom reflection pulse B2 from the bottom of the material and a second surface reflection pulse S2 from the surface of the material, .circle.16 is a measuring gate proportional to a time interval between the first bottom reflection pulse B1 and the second bottom reflection pulse B2, and .circle.17 is an output signal from the AND gate 223 which is an "and" of the measuring gate and a clock pulse signal. The number of the clock pulses output from the AND gate 223 is proportional to the thickness of the material to be measured. The pulse number of .circle.17 is counted by the counter 224 and the count result is indicated on the indicator 225 as the thickness of the material.
FIG. 12 is another example of operation waveform in the conventional thickness measuring apparatus. This example is for a measurement in which a material 204 to be measured has a large thickness and a probe used has a small delay member. In this measurement, the second surface reflection pulse S2 appears between the first bottom reflection pulse B1 and the second bottom reflection pulse B2 and the second surface reflection pulse S2 prevents accurate thickness measurement.
To solve this problem, the conventional ultrasonic thickness measuring apparatus as described above uses a CRT display 221 for selecting multiple bottom reflection pulses among multiple reflection pulses from the surface and the bottom of the material 204 to be measured. More particularly, a delay time of the delay gate is adjusted while watching the CRT display 221 to eliminate interference by the transmission pulse and the multiple reflection pulses from the surface of the material 204 to be measured. Further, an indication position of the reflection pulses and a measuring range are checked.
In the conventional apparatus, the thickness measurement is carried out by using the measuring gate lasting from the first bottom reflection pulse B1 to the second reflection pulse B2 and counting the number of clock pulses within the measuring gate. However, a delay amount of the delay gate should be adjusted to eliminate interference by the transmission pulse T and the multiple reflection pulses from the surface of the material 204 to be measured.
Further, when the delay member attached to the probe 3 has different lengths or the sonic velocity of the delay member is varied with a variation of temperature etc., the above-mentioned adjustment are necessitated.
The conventional apparatus has such a disadvantage that the structure and the operation should inevitably be complicated and the entire size of the apparatus should be large to provide the CRT display therein and to select reflection pulses from the bottom of the material.
Therefore, the present invention has been made also to solve this problem and it is a second object of the present invention to provide an ultrasonic thickness measuring method and apparatus which is capable of assuring accurate thickness measurement, while automatically minimizing the transmission pulse and multiple reflection pulses from the surface of the material to be measured or reducing noises without using the CRT display, and automatically compensating variation of delay amount of the delay member.
In this connection, it is to be noted that contact between the probe for transmitting and receiving ultrasonic wave and the material to be measured is a very important factor of the measurement effected by the apparatus which detects reflection pulses from the material to be measured for measuring the thickness as described above.
More particularly, the ultrasonic thickness measuring apparatus measures a thickness of a material by placing the probe in contact with the material to be measured, transmitting ultrasonic pulse and detecting reflection pulses from the material to measure a thickness from the travel time of the ultrasonic pulse through the material. A check apparatus is used for such an ultrasonic thickness measuring apparatus for checking the contact conditions between the probe and the material to be measured, the couplant film conditions, acoustic coupling defects due to surface roughness of the material to be measured, breaking of the probe cable, attenuation of ultrasonic wave within the material to be measured, lowering of the ultrasonic wave transmission output, or deterioration of performance of the thickness measuring apparatus.
FIG. 16 is an explanatory view showing a conventional check apparatus for use with an ultrasonic thickness measuring apparatus. In this example, a separate type probe is used which comprises an ultrasonic transmitter and receiver.
In the figure, 302a is a separate type probe which comprises an ultrasonic transmitter and receiver formed integrally with each other, 311 is a piezoelectric vibrator effecting electric-acoustic converting, 312a is the ultrasonic transmitter, 312b is the ultrasonic receiver and 313 is a material whose thickness is to be measured.
In the check apparatus for the ultrasonic thickness measuring apparatus as described above, the separate type probe 302a is pressed against the material 313 made for example of metals through a couplant such as an oil or water applied on the surface of the material. When an ultrasonic pulse T is transmitted to the material 313 from the ultrasonic transmitter 312a, a first reflection pulse S1 from the surface of the material 313 is received by the ultrasonic transmitter 312a and a second reflection pulse B1 from the bottom of the material 313 is received by the ultrasonic receiver B1.
The thickness measurement is effected, while correcting a time interval between the first reflection pulse S1 and the second reflection pulse B1 according to a sonic velocity of the material 313. At this time, a flip-flop circuit FF is used for the measurement. The flip-flop circuit FF rises by the first reflection pulse S1 and inverts its operation by the second reflection pulse B1. If the second reflection pulse B1 obtained is not at a certain level, the flip-flop circuit FF is not inverted. Therefore, the second reflection pulse B1 can be checked by monitoring the inversion of the flip-flop circuit FF.
FIG. 17 is a similar explanatory view showing another check apparatus utilizing a single reflection pulse according to single probe technique using a single transducer.
In the figure, 311 is the piezoelectric vibrator, 313 is the material to be measured and 302 is a probe for transmitting and receiving ultrasonic pulses.
The piezoelectric vibrator 311 of the probe 302 is pressed against the material 313 to be measured and an ultrasonic pulse T is transmitted to the material 313. The ultrasonic pulse travels through the material and a reflection pulse B1 from the bottom of the material is received by the probe 302. The measurement of the thickness of the material 313 is effected, while correcting the time interval between the ultrasonic pulse T and the reflection pulse B1 from the bottom according to the sonic velocity. To carry out the measurement accurately, a check appratus is employed in which the level of the reflection pulse B1 is observed by the CRT display.
FIG. 18 is an explanatory view showing a further example of a conventional check apparatus for an ultrasonic thickness measuring apparatus.
In this example, single probe technique utilizing multiple reflection pulses is employed.
According to this example, multiple pulses which are obtained from an ultrasonic pulse T transmitted by the probe 302 and travelled through the material 313 are utilized, a first reflection pulse B1 from the bottom and a second reflection pulse B2 from the bottom are received and a time interval between the reflection pulses is corrected according to the sonic velocity of the material 313 to measure the thickness.
At this time, levels of the first reflection pulse B1 and the second reflection pulse B2 are observed by a CRT display to check the pulses. The CRT display employed is for example a CRT display 118 as shown in FIG. 6.
FIG. 19 is an explanatory view showing a still further example of a conventional check apparatus for an ultrasonic thickness measuring apparatus.
This example employs a probe with a delay member according to single probe technique.
In the figure, 302b is a probe having a member giving a delay to ultrasonic wave propagation which is provided on a radiation face of a piezoelectric vibrator 311 and 312 is the delay member made, for example, of acrylic materials.
When an ultrasonic pulse T is transmitted from the probe 302b to the material 313 to be measured, a first reflection pulse S1 from a surface of the material 313, a second reflection pulse B1 which is a first reflection pulse from a bottom of the material 313, a third reflection pulse B2 which is a second reflection pulse from the bottom and a fourth reflection pulse S2 which is a second reflection pulse from the surface of the material 313 are received by the probe 302b.
The measurement of the thickness is effected, while correcting a time interval between the second reflection pulse B1 and the third reflection pulse B2 according to a sonic velocity of the material 313. At this time, levels of the second reflection pulse B1 and the third reflection pulse B2 are observed by using a CRT to check them.
These conventional check apparatuses as described above, however, has the following problems.
In the case where the separate type probe 302a is employed, check is made only by the second reflection pulse B1 from the bottom of the material, but check is not made by the first reflection pulse S1.
In the case where single probe technique is employed, the operation check is made by observing the reflection pulses used for the thickness measurement on the CRT display. Thus, the CRT display should be provided and the entire configuration becomes complicated and large.
Further, the conventional check apparatus should have different configurations for different kinds of the probes or thickness measurement techniques, so that the CRT display should be adjusted according to the thickness of the material to be measured or a change of the sonic velocity of the material.
It is therefore a third object of the present invention to provide a check apparatus for an ultrasonic thickness measuring apparatus which is capable of automatically indicating the check results for the reflection pulses utilized in the measurement without making any adjustment, even when the thickness or sonic velocity of the material to be measured or the kind of the probe or thickness measurement technique is changed.